Metal-Oxide-Semiconductor (MOS) transistor is one of the most important components in modern integrated circuits. The basic structure of the MOS transistor includes a semiconductor substrate, a gate structure formed on the semiconductor substrate, a source region formed at one side of the gate structure, and a drain region formed at other side of the gate structure. The gate structure includes a gate dielectric layer formed on the semiconductor substrate, and a gate electrode layer formed on the gate dielectric layer. The source region and the drain region are doped with ions.
With the increasing of integration degree of the MOS transistor, the voltage and current required for operating the MOS transistor continue to reduce, and the switching speed of the transistor accelerates accordingly, thus more requirements of the semiconductor fabrication process are substantially needed. Therefore, high dielectric constant material (high-K material) has been used instead of SiO2 as a gate dielectric layer to better isolate the gate structure and the other parts of the MOS transistor, and to reduce leakage current. At the same time, to be compatible with the high-K (K larger than 3.9) dielectric constant material, metal material has been used instead of the original polysilicon as the gate electrode layer. The high-K gate dielectric layer and the metal gate electrode form a metal gate structure, so as to further reduce the leakage current of the MOS transistor.
A gate-last process is usually used to form the MOS transistor having the metal gate structure. During the gate-last process, a dummy gate structure is first formed on the semiconductor substrate, and an interlayer dielectric layer is formed on the semiconductor substrate at both sides of the dummy gate structure. The top surface of the interlayer dielectric layer is leveled with the top surface of the dummy gate structure. Then the dummy gate electrode is removed, and the metal gate electrode is formed at a position previously defined by the dummy gate electrode.
However, the height of the metal gate electrode cannot be controlled by the existing techniques to form the semiconductor device. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.